1. Field of the Invention
This invention relates to a method and device for the preparation of a solute (herein defined as a material which may comprise one or more components) that it is desired to isolate and purify for induction into analytical instruments such as cas chromatographs (GC), ultra-violet (UV) and infra-red (IR) spectographs, etc. In accordance with this invention a solute, liquid or gas is prepared to a sufficient level of concentration and purity for facile analysis, even when such solution exists in a solvent/matrix in the low parts-per-billion (ppb) range; that is, the picogram range. The concentrating/purifying process of this invention is accomplished by use of a serial, sequential, differential trapping arrangement which allows the solvent, which may be liquid or gas, to pass through to vent while retaining the solute. The solute is then backflushed/heat-desorbed from the trapping system and transferred to another analytical device, generally a gas chromatograph (GC), where it may be analyzed. When a GC is used, either packed or capillary columns may be used as a component separating device.
2. Description of the Prior Art
At present, the state-of-the-art relating to trace analysis in the low ppb range, utilizing traditional gas chromatography techniques with existing hardware and materials, generally has been inadequate, sometimes requiring extensive and time consuming methods which are costly. In many cases low ppb range analyses is not capable of economic attainment by available standard methods.
The major constraint to low-ppb analysis, following conventional gas chromatographic practice, is column capacity. Typically, the maximum sample size that normally can be inputted to a gas chromatograph column is 10 .mu.l liquid or 5 cc gas. When the solute: solvent ratios are extremely low, the foregoing sample sizes may not contain enough of the solutes(s) for measurement. This of course is dependent on sample size versus detector sensitivity. Larger sample sizes frequently result in solvent interference, peak spreading, poor resolution, etc., thereby precluding satisfactory analysis.
The prior art has not heretofore appreciated that utilization of a series of serial sequentially connected traps operated in the differential trapping mode, provides increased solute purity and the ability to increase solute sample size. When coupled with appropriate monitoring and control means, the differential trapping system can provide a high order of analytical data for solute(s) contained within the broad spectrum of physically divergent samples.
The use of multiport valve-trap arrangements has heretofore been employed (see e.g. U.S. Pat. Nos. 3,955,924; 3,847,546) and multiple arrangements of such multiport valve-trap systems have been used both in parallel (see U.S. Pat. No. 3,693,403) and in series (See U.S. Pat. No. 3,545,255); however, the art has not heretofore appreciated that concentration of solute(s) within a sample could be effected in a highly facile and advantageous manner by utilizing serial, sequential differential trapping to obtain a high order of concentrate along with good sample purity and integrity to perform an unimpeded analysis.